System and method for improving resolution of digital seismic images

ABSTRACT

A method is described for seismic imaging including receiving a seismic dataset representative of a subsurface volume of interest and an earth model; decomposing the seismic dataset into a set of data sub-sets based on a decomposition function; imaging each data sub-set using the earth model to generate a set of image sub-sets; and combining the set of image sub-sets based on a criterion to create a high resolution seismic image. The method may be executed by a computer system.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD

The disclosed embodiments relate generally to techniques for improvingthe resolution of digital seismic images of the Earth's subsurface and,in particular, to a method of improving the resolution of digitalseismic images of subsurface geologic features using data and/or imagedecomposition.

BACKGROUND

Seismic exploration involves surveying subterranean geological media forhydrocarbon deposits. A survey typically involves deploying seismicsources and seismic sensors at predetermined locations. The sourcesgenerate seismic waves, which propagate into the geological mediumcreating pressure changes and vibrations. Variations in physicalproperties of the geological medium give rise to changes in certainproperties of the seismic waves, such as their direction of propagationand other properties.

Portions of the seismic waves reach the seismic sensors. Some seismicsensors are sensitive to pressure changes (e.g., hydrophones), others toparticle motion (e.g., geophones), and industrial surveys may deploy onetype of sensor or both. In response to the detected seismic waves, thesensors generate corresponding electrical signals, known as traces, andrecord them in storage media as seismic data. Seismic data will includea plurality of “shots” (individual instances of the seismic source beingactivated), each of which are associated with a plurality of tracesrecorded at the plurality of sensors.

Seismic data is processed to create seismic images that can beinterpreted to identify subsurface geologic features includinghydrocarbon deposits. Conventional imaging techniques such as migrationproduce seismic images with resolution that is limited by the frequencyof the data and the accuracy of the earth model used by the imaging. Theability to define the location of rock and fluid property changes in thesubsurface is crucial to our ability to make the most appropriatechoices for purchasing materials, operating safely, and successfullycompleting projects. Project cost is dependent upon accurate predictionof the position of physical boundaries within the Earth. Decisionsinclude, but are not limited to, budgetary planning, obtaining mineraland lease rights, signing well commitments, permitting rig locations,designing well paths and drilling strategy, controlling production andinjection rates, preventing subsurface integrity issues by planningproper casing and cementation strategies, and selecting and purchasingappropriate completion and production equipment.

There exists a need for improved resolution in seismic images that willallow better seismic interpretation of potential hydrocarbon reservoirsso that the hydrocarbons can be produced.

SUMMARY

In accordance with some embodiments, a method of seismic imagingincluding receiving a seismic dataset representative of a subsurfacevolume of interest and an earth model; decomposing the seismic datasetinto a set of data sub-sets based on a decomposition function; imagingeach data sub-set using the earth model to generate a set of imagesub-sets; and combining the set of image sub-sets based on a criterionto create a high resolution seismic image is disclosed.

In another aspect of the present invention, to address theaforementioned problems, some embodiments provide a non-transitorycomputer readable storage medium storing one or more programs. The oneor more programs comprise instructions, which when executed by acomputer system with one or more processors and memory, cause thecomputer system to perform any of the methods provided herein.

In yet another aspect of the present invention, to address theaforementioned problems, some embodiments provide a computer system. Thecomputer system includes one or more processors, memory, and one or moreprograms. The one or more programs are stored in memory and configuredto be executed by the one or more processors. The one or more programsinclude an operating system and instructions that when executed by theone or more processors cause the computer system to perform any of themethods provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of a method of seismic imaging, inaccordance with some embodiments;

FIG. 2 illustrates a flowchart of a method of seismic imaging, inaccordance with other embodiments;

FIG. 3 illustrates a flowchart of a method of seismic imaging, inaccordance with other embodiments;

FIG. 4 illustrates a wedge model, seismic data, prior art results, andresults of an embodiment of the present invention;

FIG. 5 illustrates the improvement in the spatial spectrum resultingfrom an embodiment as compared with the prior art;

FIG. 6 illustrates another result of an embodiment; and

FIG. 7 is a block diagram illustrating a seismic imaging system, inaccordance with some embodiments.

Like reference numerals refer to corresponding parts throughout thedrawings.

DETAILED DESCRIPTION OF EMBODIMENTS

Described below are methods, systems, and computer readable storagemedia that provide a manner of seismic imaging. These embodiments aredesigned to be of particular use for seismic imaging of subsurfacevolumes in geologically complex areas.

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings. In the followingdetailed description, numerous specific details are set forth in orderto provide a thorough understanding of the present disclosure and theembodiments described herein. However, embodiments described herein maybe practiced without these specific details. In other instances,well-known methods, procedures, components, and mechanical apparatushave not been described in detail so as not to unnecessarily obscureaspects of the embodiments.

Seismic imaging of the subsurface is used to identify potentialhydrocarbon reservoirs. Seismic data is acquired at a surface (e.g. theearth's surface, ocean's surface, or at the ocean bottom) as seismictraces which collectively make up the seismic dataset. Seismic imagingtechniques generally use an earth model (a model of the subsurfaceincluding at least P-wave velocity V_(p), and optionally S-wave velocityV_(s) and/or density, along with other possible properties such aslithology) to transform the seismic data into a seismic image. Theseismic image will have a vertical and horizontal resolution (i.e.seismic resolution) that is dependent on the frequency content of theseismic dataset and the accuracy of the earth model. However, in theearth's subsurface, many features may exist that are smaller than can beseen at the seismic resolution. Conventional seismic imaging often willfail to resolve fine features in the subsurface that may containinformation on stratigraphy and structure.

The present invention includes embodiments of a method and system forseismic imaging with improved resolution. The present invention producesseismic images with greater resolution than conventional methods,allowing for evaluation and validation of seismic interpretations of thesubsurface.

FIG. 1 illustrates a flowchart of a method 100 for seismic imaging of asubsurface volume of interest. At operation 10, a seismic dataset isreceived. As previously described, the seismic dataset includes aplurality of traces recorded at a plurality of seismic sensors. Thisdataset may have already been subjected to a number of seismicprocessing steps, such as deghosting, multiple removal, spectralshaping, and the like. These examples are not meant to be limiting.Those of skill in the art will appreciate that there are a number ofuseful seismic processing steps that may be applied to seismic databefore it is deemed ready for imaging. An earth model representative ofthe subsurface is also received. The earth model includes, at a minimum,the P-wave velocity model (V_(p)). Although the velocity model is someform of “best guess”, those of skill in the art are aware that velocitymodels often contain errors, particularly in complex areas of thesubsurface.

At operation 12, the seismic data is decomposed into a set of datasub-sets based on a decomposition function. This may be done, by way ofexample and not limitation, as a function of time or depth. In anembodiment, it may be done as a function of extracting the maximumamplitude of the calculated seismic trace, function of extracting theinstantaneous amplitude of the seismic trace, function of the calculatedtravel times by ray-tracing. The decomposition function may be labeledsuch that it indicates lithologic facies. These labels may be useful formachine-learning algorithms designed to classify regions or volumes ofthe dataset and allows for projection of the labels into the datadomain.

At operation 14, each data sub-set is subjected to seismic imaging, suchas reverse time migration (RTM) or a similar imaging technique, togenerate a set of seismic images. The advantage of imaging each datasub-set is the ability to focus on imaging the (stratigraphic) featureof interest. Then the set of seismic images is combined at operation 16into a single seismic image based on a criterion such as spatialspectral improvement. The images from each sub-set can be stacked(summed) with and/or without a pre-specified stacking weight. Theresulting seismic image will have higher resolution than the seismicimage that would have been obtained by imaging the original seismicdataset.

The image subsets from operation 14 may be analyzed to identifymisalignment between the same events in the individual subsets. Thesemisalignments may be used to identify areas where there are errors inthe earth model. Similarity metrics such as cross-gradient can be usedto identify misalignment between the individual subsets.

FIG. 2 illustrates another embodiment of a method 200 for seismicimaging. In this embodiment, a digital seismic image and an earth modelare received at operation 20. The digital seismic image was generatedfrom a seismic dataset using any seismic imaging technique. In someembodiments, the seismic image may be flattened on a seismic horizon,using a method such as based on the method described by U.S. Pat. No.7,769,546, Method for Indexing a Subsurface Volume For The Purpose ofInferring Geologic Information, or U.S. patent application Ser. No.14/595,964, System and Method for Generating a Depositional SequenceVolume from Seismic Data. The earth model includes at least the V_(p)model for the subsurface.

At operation 22, the seismic image is decomposed into a set of imagesub-sets based on a decomposition function. This may be done, by way ofexample and not limitation, as a function of time or depth. In anembodiment, it may be done as an extraction of a single depth/stratalslice. The decomposition function may be labeled such that it indicateslithologic facies. These labels may be useful for machine-learningalgorithms designed to classify regions or volumes of the dataset andallows for projection of the labels into the data domain.

At operation 24, each of the image sub-sets is forward-modeled togenerate a synthetic seismic dataset, creating a set of synthetic datasub-sets. The forward modeling may be done, for example, byfinite-difference Born modeling.

At operation 26, each of the synthetic data sub-set is subjected toseismic imaging, such as reverse time migration (RTM) or a similarimaging technique, to generate a set of seismic images. The imaging eachdata sub-set stems from the ability to avoid seismic interferencebetween features from above and below the specified depth. Then the setof seismic images is combined at operation 28 into a single seismicimage based on a criterion such as spatial spectral improvement. Theimages from each sub-set can be stacked (summed) with and/or without apre-specified stacking weight. The resulting seismic image will havehigher resolution than the input seismic image.

The set of synthetic data sub-sets from operation 24 may be analyzed toidentify subsurface structures and/or stratigraphic patterns. By way ofexample and not limitation, computer algorithms using artificialintelligence may be used to identify stratigraphic patterns.

FIG. 3 shows yet another embodiment as method 300. Method 300 is acombination of methods 100 and 200. At operation 30, a seismic image ofthe subsurface volume of interest is received. An earth modelrepresentative of the subsurface is also received. The earth modelincludes, at a minimum, the P-wave velocity model (V_(p)).

At operation 31, the seismic image is decomposed into a set of imagesubsets based on an image-domain decomposition function. This may bedone, by way of example and not limitation, as a function of time,depth, or source-receiver trace number.

At operation 32, each of the image subsets is forwarded modeled togenerate a synthetic seismic dataset, creating a set of synthetic datasubsets. The forward modeling may be done, for example, byfinite-difference Born modeling.

At operation 33, each data subset in the set of synthetic data subsetsis decomposed into data sub-subsets based on a data-domain decompositionfunction. This data-domain decomposition function may be, by way ofexample and not limitation, a function of time. In an embodiment, it maybe done as a function based on travel time calculations.

At operation 34, each data sub-subset is subjected to seismic imaging,such as RTM or a similar imaging technique, to generate a set of seismicimages, resulting in sets of image sub-subsets. Optionally, some ofthese sets of image sub-subsets may be selected by the user to becombined at operation 35 into image subsets. In this embodiment, theuser may select sets of image sub-subsets based on previous geologicinterpretation of the subsurface volume of interest, possibly fromprevious seismic images.

The set of image subsets (or image sub-subsets if operation 35 was notperformed) are combined at operation 36 into a single seismic imagebased on a criterion such as improved spatial spectra. The resultingseismic image will have higher resolution than the original seismicimage received at operation 30. At the decision block 37, if theresolution of the seismic image is sufficient, the process ends. If not,the process returns to operation 31 and operations 31 through 36 arerepeated.

Method 300 may optionally be performed with more than one earth model asinput. In that case, the process performs the imaging of the datasub-subsets 34 using each earth model to make multiple sets of imagesub-subsets. These may be combined using a criterion to improve spatialspectra.

For any of the above embodiments, the next step is to interpret theseismic image. When interpreting a seismic image, seismic horizons areidentified and traced throughout the subsurface volume of interest.Improving the resolutions of events allows better interpretation. Thismay impact hydrocarbon reservoir delineation and well planning.

An example of an embodiment can be seen in FIG. 4. The true model isshown in the top row, including a horizontal reflector, a dippingreflector, and a combination of the two to form a wedge model. Thesecond row shows a shot gather that was forward-modeled for each model.Images obtained using a prior art imaging technique can be seen in thethird row. The fourth row shows results using a present embodiment. Inparticular, the images for the dipping reflector and the wedge reflectorare better focused in the result from the present embodiment.

FIG. 5 demonstrates the wavenumber-domain difference between the priorart result and the result of the present embodiment. Note that the priorart result extends to wavenumbers of about 30 km⁻¹ while the result ofthe present embodiment extends to about 42 km⁻¹. These higherwavenumbers mean that the image is better focused with higherresolution.

FIG. 6 is another example of an embodiment. The depth slice of theoriginal image on the left is poorly focused when compared with theresult of a present embodiment, shown as the depth slice of the newimage. The depth slice of the true impedance model is on the right anddepicts a channel system. The new image from the present invention aremore easily interpretable that the original image.

FIG. 7 is a block diagram illustrating a seismic imaging system 600, inaccordance with some embodiments. While certain specific features areillustrated, those skilled in the art will appreciate from the presentdisclosure that various other features have not been illustrated for thesake of brevity and so as not to obscure more pertinent aspects of theembodiments disclosed herein.

To that end, the seismic imaging system 600 includes one or moreprocessing units (CPUs) 502, one or more network interfaces 508 and/orother communications interfaces 503, memory 506, and one or morecommunication buses 504 for interconnecting these and various othercomponents. The seismic imaging system 600 also includes a userinterface 505 (e.g., a display 505-1 and an input device 505-2). Thecommunication buses 504 may include circuitry (sometimes called achipset) that interconnects and controls communications between systemcomponents. Memory 506 includes high-speed random access memory, such asDRAM, SRAM, DDR RAM or other random access solid state memory devices;and may include non-volatile memory, such as one or more magnetic diskstorage devices, optical disk storage devices, flash memory devices, orother non-volatile solid state storage devices. Memory 506 mayoptionally include one or more storage devices remotely located from theCPUs 502. Memory 506, including the non-volatile and volatile memorydevices within memory 506, comprises a non-transitory computer readablestorage medium and may store seismic data, velocity models, seismicimages, and/or geologic structure information.

In some embodiments, memory 506 or the non-transitory computer readablestorage medium of memory 506 stores the following programs, modules anddata structures, or a subset thereof including an operating system 516,a network communication module 518, and a seismic imaging module 520.

The operating system 516 includes procedures for handling various basicsystem services and for performing hardware dependent tasks.

The network communication module 518 facilitates communication withother devices via the communication network interfaces 508 (wired orwireless) and one or more communication networks, such as the Internet,other wide area networks, local area networks, metropolitan areanetworks, and so on.

In some embodiments, the seismic imaging module 520 executes theoperations of methods 100, 200, and/or 300. Seismic imaging module 520may include data sub-module 525, which handles the seismic datasetincluding seismic gathers 525-1 through 525-N. This seismic data issupplied by data sub-module 525 to other sub-modules.

Decomposition sub-module 522 contains a set of instructions 522-1 andaccepts metadata and parameters 522-2 that will enable it to executedecomposition operations for methods 100, 200, and/or 300. The forwardmodeling sub-module 523 contains a set of instructions 523-1 and acceptsmetadata and parameters 523-2 that will enable it to perform forwardmodeling as needed for methods 100, 200, and/or 300. The imagingsub-module 524 contains a set of instructions 524-1 and accepts metadataand parameters 524-2 that will enable it to perform imaging as neededfor methods 100, 200, and/or 300. Although specific operations have beenidentified for the sub-modules discussed herein, this is not meant to belimiting. Each sub-module may be configured to execute operationsidentified as being a part of other sub-modules, and may contain otherinstructions, metadata, and parameters that allow it to execute otheroperations of use in processing seismic data and generate the seismicimage. For example, any of the sub-modules may optionally be able togenerate a display that would be sent to and shown on the user interfacedisplay 505-1. In addition, any of the seismic data or processed seismicdata products may be transmitted via the communication interface(s) 503or the network interface 508 and may be stored in memory 506.

Method 100 is, optionally, governed by instructions that are stored incomputer memory or a non-transitory computer readable storage medium(e.g., memory 506 in FIG. 6) and are executed by one or more processors(e.g., processors 502) of one or more computer systems. The computerreadable storage medium may include a magnetic or optical disk storagedevice, solid state storage devices such as flash memory, or othernon-volatile memory device or devices. The computer readableinstructions stored on the computer readable storage medium may includeone or more of: source code, assembly language code, object code, oranother instruction format that is interpreted by one or moreprocessors. In various embodiments, some operations in each method maybe combined and/or the order of some operations may be changed from theorder shown in the figures. For ease of explanation, method 100 isdescribed as being performed by a computer system, although in someembodiments, various operations of method 100 are distributed acrossseparate computer systems.

While particular embodiments are described above, it will be understoodit is not intended to limit the invention to these particularembodiments. On the contrary, the invention includes alternatives,modifications and equivalents that are within the spirit and scope ofthe appended claims. Numerous specific details are set forth in order toprovide a thorough understanding of the subject matter presented herein.But it will be apparent to one of ordinary skill in the art that thesubject matter may be practiced without these specific details. In otherinstances, well-known methods, procedures, components, and circuits havenot been described in detail so as not to unnecessarily obscure aspectsof the embodiments.

The terminology used in the description of the invention herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the invention. As used in the description ofthe invention and the appended claims, the singular forms “a,” “an,” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will also be understood that theterm “and/or” as used herein refers to and encompasses any and allpossible combinations of one or more of the associated listed items. Itwill be further understood that the terms “includes,” “including,”“comprises,” and/or “comprising,” when used in this specification,specify the presence of stated features, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, operations, elements, components, and/or groups thereof.

As used herein, the term “if” may be construed to mean “when” or “upon”or “in response to determining” or “in accordance with a determination”or “in response to detecting,” that a stated condition precedent istrue, depending on the context. Similarly, the phrase “if it isdetermined [that a stated condition precedent is true]” or “if [a statedcondition precedent is true]” or “when [a stated condition precedent istrue]” may be construed to mean “upon determining” or “in response todetermining” or “in accordance with a determination” or “upon detecting”or “in response to detecting” that the stated condition precedent istrue, depending on the context.

Although some of the various drawings illustrate a number of logicalstages in a particular order, stages that are not order dependent may bereordered and other stages may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beobvious to those of ordinary skill in the art and so do not present anexhaustive list of alternatives. Moreover, it should be recognized thatthe stages could be implemented in hardware, firmware, software or anycombination thereof.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A computer-implemented method of seismic imaging,comprising: a. receiving, at a computer processor, a seismic datasetrepresentative of a subsurface volume of interest and an earth model; b.decomposing the seismic dataset into a set of data sub-sets based on adecomposition function wherein the decomposition function is a functionof time or depth and is one of a function of extracting maximumamplitudes of seismic traces in the seismic dataset, a function ofextracting instantaneous amplitudes of seismic trace in the seismicdataset, or a function of calculated travel times by ray-tracing in theearth model; c. imaging each data sub-set using the earth model togenerate a set of image sub-sets; and d. combining the set of imagesub-sets based on a criterion to create a high resolution seismic image.2. The method of claim 1 wherein the earth model is a velocity model. 3.The method of claim 2 further comprising analyzing the set of imagesub-sets to identify misalignment indicating velocity errors in thevelocity model.
 4. The method of claim 1 wherein the decomposing is doneas a function of time.
 5. The method of claim 1 further comprisinglabeling the decomposition function.
 6. The method of claim 1 whereinthe criterion is spatial spectra improvement.
 7. The method of claim 1further comprising identifying geological features based on the highresolution seismic image.
 8. The method of claim 1 further comprisingusing the high resolution seismic image to control at least one ofdrilling a production well and/or drilling an injection well.
 9. Acomputer system, comprising: a. one or more processors; b. memory; andc. one or more programs, wherein the one or more programs are stored inthe memory and configured to be executed by the one or more processors,the one or more programs including instructions that when executed bythe one or more processors cause the device to: receive, at the one ormore processors, a seismic dataset representative of a subsurface volumeof interest and an earth model; decompose the seismic dataset into a setof data sub-sets based on a decomposition function wherein thedecomposition function is a function of time or depth and is one of afunction of extracting maximum amplitudes of seismic traces in theseismic dataset, a function of extracting instantaneous amplitudes ofseismic trace in the seismic dataset, or a function of calculated traveltimes by ray-tracing in the earth model; image each data sub-set usingthe earth model to generate a set of image sub-sets; combine the set ofimage sub-sets based on a criterion to create a high resolution seismicimage; and identify geologic features based on the high-resolutionseismic image.
 10. A non-transitory computer readable storage mediumstoring one or more programs, the one or more programs comprisinginstructions, which when executed by an electronic device with one ormore processors and memory, cause the device to receive, at the one ormore processors, a seismic dataset representative of a subsurface volumeof interest and an earth model; decompose the seismic dataset into a setof data sub-sets based on a decomposition function wherein thedecomposition function is a function of time or depth and is one of afunction of extracting maximum amplitudes of seismic traces in theseismic dataset, a function of extracting instantaneous amplitudes ofseismic trace in the seismic dataset, or a function of calculated traveltimes by ray-tracing in the earth model; image each data sub-set usingthe earth model to generate a set of image sub-sets; and combine the setof image sub-sets based on a criterion to create a high resolutionseismic image; and identify geologic features based on thehigh-resolution seismic image.